br Introduction Cystic Fibrosis CF is an autosomal recessive

Introduction Cystic Fibrosis (CF) is an autosomal recessively inherited disease most prevalent in Caucasian populations of European origin (World Health Organization, 2004). In the UK about 10,000 people have CF, globally about 70–100,000 people are affected (World Health Organization, 2004). Although CF is a multisystem condition the majority of CF associated morbidity and mortality is a consequence of chronic suppurative lung disease and ultimately respiratory failure (UK CF Registry, 2014; Goss and Quittner, 2007), currently median (95% CI) age of death in the UK is 29 (27–31) (UK CF Registry, 2014). Infection of the lower airways by Pseudomonas (Emerson et al., 2002), and Burkholderia species (Muhdi et al., 1996; Jones et al., 2004) adversely affects morbidity, quality of life and survival, and there are increasing concerns about the consequences of infection with emergent (Lipuma, 2010) pathogen species such as Mycobacterium abscessus (Esther et al., 2010; Hansen et al., 2006). In CF, Pseudomonas (Emerson et al., 2002) and Burkholderia (Muhdi et al., 1996; Jones et al., 2004) species grow in biofilms and as such are much more resistant to TASIN-1 compared with planktonic-growing cells of the same isolate (Stewart and Costerton, 2001). The aggressive use of antibiotics to suppress chronic infection and to treat acute exacerbations has contributed to the increased survival of people with CF. However, increasing antibiotic resistance, multiple antibiotic resistance and drug intolerance are emerging as major clinical problems. These issues have led to calls for research into new antimicrobial agents and new antibiotic strategies to target the biofilm and to increase the effectiveness of currently available antibiotics (Bals et al., 2011). We have previously described the in vitro antimicrobial, anti-biofilm and mucoactive properties of cysteamine as a monotherapy and in combination with CF guideline recommended antibiotics (Charrier et al., 2014). Cysteamine has been routinely used to treat cystinosis for more than 20years and so a significant body of clinical data already exists as to its characteristics within this patient group. The antimicrobial and mucoactive attributes of cysteamine described to date are potentially therapeutically beneficial in CF, not only in the treatment of acute exacerbations but also chronic management (Charrier et al., 2014). An inherent limitation of the data derived thus far is that they were generated from monocultures of bacteria most commonly isolated from people with CF and against individual components of mucus. To investigate the potential of cysteamine in CF under more physiologically robust conditions, we investigated its mucolytic and antimicrobial activity against sputum from CF patients and report here for the first time on its rheological properties and antimicrobial action against the polymicrobial content of CF sputum. We also report on the activity of cysteamine against M. abscessus isolates from CF participants in this study.
Methods and Materials
Results
Discussion Cysteamine is an aminothiol (HSCH2CH2NH2) endogenously present at very low levels as a consequence of coenzyme A metabolism (Besouw et al., 2013; Orloff et al., 1981). In the US and EU, cysteamine has been licensed for the treatment of nephropathic cystinosis for over 20years. In this observational study the in vitro antimicrobial and mucoactive properties of cysteamine were tested in sputum samples from adults with CF infected with bacteria typical of those reported in the UK CF population (Staphylococcus aureus, P. aeruginosa, Burkholderia species and Stenotrophomonas maltophilia). Cysteamine reduced sputum polymicrobial load ex vivo and at the doses tested this antimicrobial effect was greater than that observed for tobramycin and ciprofloxacin. The combination of cysteamine with tobramycin appeared to be more than additive after 24h incubation, being greater than the individual effects of cysteamine or tobramycin. The combination of cysteamine/ciprofloxacin appeared to be no more antimicrobial than cysteamine alone, although we have previously demonstrated a synergistic interaction for these two compounds in vitro (Charrier et al., 2014). Whilst the lack of synergy between cysteamine and ciprofloxacin may merely be a consequence of the small number of sputum samples analysed (n=9), it may be that in the matrix of sputum the combination of cysteamine/ciprofloxacin is unable to exert the additive effect present when cultured under standard media conditions, further work is required to investigate whether in vivo there is synergy between cysteamine and ciprofloxacin. In our present study, we also demonstrated that M. abscessus is sensitive to cysteamine; more so than for other CF bacteria when tested in vitro as a monotherapy. Cysteamine also potentiates the activity of other antimicrobial agents. In addition to cysteamine\'s antimicrobial effects, in vitro, cysteamine had mucolytic effects, reducing sputum viscosity 8–9 fold, notably cysteamine had more potent (6–7 fold) mucolytic effect than recombinant DNAse. We demonstrated that the antimicrobial effects of cysteamine were not modified by clinical factors e.g. sex, lung function, exacerbation status nor by concurrent medication e.g. azithromycin, inhaled antibiotics or ivacaftor. However, these analyses were of small numbers of patients and lacked statistical power, further work is required to determine whether any antimicrobial effects of cysteamine are modified by concurrent medications, or other factors e.g. disease severity, sex, age.